Method of fabricating probe for spm having fet channel structure utilizing self-aligned fabrication

ABSTRACT

Provided is a method of fabricating a probe for a scanning probe microscope (SPM) having a field effect transistor (FET) channel structure utilizing a self-aligned fabrication. The provided method includes a first step of forming a first-shaped mask layer on a substrate and forming a source region and a drain region in regions of the substrate except for the mask layer; a second step of patterning a first-shaped photoresist in a perpendicular direction to the mask layer and performing an etching process to form a second-shaped mask layer; and a third step of etching the regions of the substrate except for the mask layer to form a probe. The provided method aligns the center of a tip with the center of a channel existing between the source region and the drain region to realize a tip having a size of tens of nanometers. Thus, a nano-device can be easily manufactured using the probe having the tip.

BACKGROUND OF THE INVENTION

This application claims the benefit of Korean Patent Application No.2002-25399, filed on May 8, 2002, in the Korean Intellectual PropertyOffice, the disclosure of which is incorporated herein in its entiretyby reference.

1. Field of the Invention

The present invention relates to a method of fabricating a probe for ascanning probe microscope (SPM) having a field effect transistor (FET)channel structure, and more particularly, to a method of fabricating aprobe for an SPM in order to easily fabricate a nano-device.

2. Description of the Related Art

Nowadays, as demands of small products, such as mobile communicationterminals and electronic notebooks, increase, the need for small-sizedand highly integrated nonvolatile recording media also increases. Sinceit is difficult to reduce the size of existing hard disks and to highlyintegrate flash memories, information storage apparatuses using scanningprobes and methods thereof have been studied.

Probes can be utilized in various SPM technologies, for example, ascanning tunneling microscope (STM) for reproducing information bydetecting currents that flow according to the difference between avoltage applied to a probe and a voltage applied to a specimen, anatomic force microscope (AFM) using an atomic force between a probe anda specimen, a magnetic force microscope (MFM) using a force between amagnetic field of a specimen and a magnetized probe, a scanningnear-field optical microscope (SNOM) improving a limit in resolution dueto the wavelength of visible rays, and an electrostatic force microscope(EFM) using static electricity between a specimen and a probe.

In order to record and reproduce high-density information at high speedby using the SPM technologies, surface charges existing in a small areaof tens of nanometers should be detected. In addition, a cantilever ofan array shape should be manufactured in order to improve recording andreproducing speeds.

FIGS. 1A and 1B are a perspective view and an enlarged view of a probefor an SPM having an FET channel structure according to Korean PatentNo. 2001-45981.

Referring to FIG. 1A, a bar-shape probe 10 formed by etching asemiconductor substrate 20 is protruded from the substrate 20, andelectrode pads 20 a and 20 b are arranged at both sides of an endportion where the probe 10 and the substrate 20 are connected.

Referring to FIG. 1B, an enlarged view of portion A in FIG. 1A, sourceand drain regions 11 and 13 are formed on an inclined surface at the endof a V-shape tip of the probe 10. In addition, a channel region 12 isformed between the source and the drain regions 11 and 13.

Since the tip of the probe is located at the end of a cantilever, it isdifficult to manufacture an array-shape cantilever and the tip having aradius of tens of nanometers. In a conventional method, a tip having aradius of tens of nanometers is manufactured using various processes,such as an oxidation process, so that the tip is vertically formed onthe cantilever.

However, the precision of a photolithographic process deteriorates whena tip having a height of several micrometers is formed, so it isdifficult to form source and drain regions having a short channellength. In addition, even when the short channel length is realizedusing a diffusion process, it is difficult to align the center of theshort channel at the end of the tip due to an alignment error in thephotolithographic process.

SUMMARY OF THE INVENTION

The present invention provides a method of fabricating a probe for ascanning probe microscope (SPM) having a field effect transistor (FET)channel structure utilizing a self-aligned fabrication to form a tiphaving a source and a drain with a short channel length at the end andhaving the center of the channel aligned at the end.

According to an aspect of the present invention, there is provided amethod of fabricating a probe comprising a first step of forming afirst-shaped mask layer on a substrate and forming a source region and adrain region in regions of the substrate except for the region masked bythe mask layer; a second step of patterning a first-shaped photoresistin a perpendicular direction to the mask layer and performing an etchingprocess to form a second-shaped mask layer; and a third step of etchingthe regions of the substrate except for the region masked by the masklayer to form a probe.

It is preferable that the first-shaped mask layer is a striped-shapedmask layer.

It is preferable that the second-shaped mask layer is a square-shapedmask layer.

It is preferable that the first step further comprises performing athermal diffusion process to reduce the distance between the sourceregion and the drain region.

When the ions are n-type ions, the substrate is a p-type substrate. Whenthe ions are p-type ions, the substrate is an n-type substrate.

BRIEF DESCRIPTION OF THE DRAWINGS

The above and other features and advantages of the present inventionwill become more apparent by describing in detail exemplary embodimentsthereof with reference to the attached drawings in which:

FIG. 1A is a perspective view illustrating a probe for a scanning probemicroscope (SPM) disclosed in Korea Patent No. 2001-45981;

FIG. 1B is an enlarged view of portion A in FIG. 1A;

FIGS. 2A through 2I are perspective views illustrating a method offabricating a probe for an SPM according to an embodiment of the presentinvention; and

FIGS. 3 and 4 are views illustrating methods of reproducing informationby using a probe for an SPM, fabricated according to the presentinvention.

DETAILED DESCRIPTION OF THE INVENTION

The present invention will now be described in more detail withreference to the accompanying drawing.

FIGS. 2A through 2I are perspective views illustrating a method offabricating a probe having a field effect transistor (FET) channelstructure, according to an embodiment of the present invention.

The method includes forming source and drain regions, etching a maskinto a predetermined shape, and forming a probe. Here, the presentinvention uses a self-aligned fabrication wherein the mask used to formthe source and the drain regions is used as a mask in the etchingprocess to form the probe.

In order to form a source region S and a drain region D, aphotolithographic process and an ion implantation process as shown inFIGS. 2A and 2B, respectively, are performed.

First, as shown in FIG. 2A, a mask layer 33 a is formed on a substrate31 and a photoresist 35 a is coated on the mask layer 33 a. Thereafter,a stripe-shaped photomask 38 a is arranged on the photoresist 35 a andexposure, development, and etching processes are performed.

Next, as shown in FIG. 2B, an ion implantation process is performed onthe regions except for the stripe-shaped mask layer 33 a to form sourceand drain regions 32 and 34.

When the substrate 31 is an n-type substrate, the source and the drainregions 32 and 34 are doped with p-type ions. When the substrate 31 is ap-type substrate, the source and the drain regions 32 and 34 are dopedwith n-type ions.

Since a mask layer 33 c located on a tip 30 as shown in FIG. 2F willserve as a mask in an etching process when forming the tip 30, the widthof the mask layer 33 b of FIG. 2B should be maintained to apredetermined size. Thus, there is a limit in reducing the width of thestripe-shaped mask layer 33 a in the photolithographic process of FIG.2A.

In addition, since the width of a channel region 36 between the sourceand the drain regions 32 and 34 shown in FIG. 2H depends on the width ofa mask layer 33 c of FIG. 2G, an additional annealing process isperformed after implanting ions in the process of FIG. 2G in order toreduce the width of the channel region 36. Accordingly, the length ofthe channel region 36 between the source and the drain regions 32 and 34is reduced while maintaining the width of the mask layer 33 g.

Thereafter, a photolithographic process and an etching process areperformed as shown in FIGS. 2C and 2D, in order to change the form of amask layer 33 b to a rectangular shape.

Referring to FIG. 2C, a photoresist 35 c is coated on the substrate 31to cover the mask layer 33 b, and a stripe-shaped mask 38 c is arrangedthereon in a perpendicular direction to the mask layer 33 b. Thereafter,exposure, development, and etching processes are performed so that thephotoresist 35 c is patterned into a stripe-shaped photoresist 35 d thatis perpendicular to the mask layer 33 b, as shown in FIG. 2D.

Referring to FIG. 2D, regions of the mask layer 33 b not covered by thestripe-shaped photoresist 35 d are dry etched. Accordingly, the exposedportions of the mask layer 33 b are removed so that a rectangular masklayer 33 c is formed as shown in FIG. 2E.

Thereafter, referring to FIG. 2E, the etching process is performed toform the rectangular mask layer 33 c and to remove the strip-shapedphotoresist 35 d.

Next, a tip is formed by performing a wet or dry etching process usingthe rectangular mask layer 33 c as shown in FIG. 2F, in order to form aprobe.

Referring to FIG. 2G, the source and the drain regions 32 and 34 areformed on the inclined surfaces of the tip 30, and the mask layer 33 clocated at the peak of the tip 30. When a thermal diffusion process isperformed after the mask layer 33 c is removed, the peak of the tip 30of the probe can be sharp and the length of the channel 36 can bereduced.

Referring to FIG. 2H, the silicon layers on the left and the right sidesof the channel region 36 of the tip 30 are doped to expand the sourceand the drain regions 32 and 34. In addition, insulating layers 37 areconnected to the source and the drain regions 32 and 34 in order toinsulate portions of the upper surface of the substrate 31.

Referring to FIG. 2I, the backside of the substrate 31 is etched torelease the cantilever.

Here, the insulating layers 37 are deposited on the portions of thesilicon substrate 31, and electrodes 39 formed on the insulating layers37 are connected to the source and the drain regions 32 and 34,respectively. A cantilever 41 is extended from the silicon layer on thesubstrate 31, and the tip 30 is formed on the surface of the cantilever41 in a vertical direction.

The method of fabricating a probe according to the present inventionuses a self-aligned fabrication utilizing the mask layer used forforming the source and the drain regions 32 and 34 as a mask for formingthe tip 30 of the probe. In addition, the processes shown in FIGS. 2Athrough 2I can be used to fabricate the probe having a different shapefrom that of FIG. 2I.

Hereafter, methods of reproducing and recording information by using theprobe fabricated by the method according to the present invention willbe described with reference to FIGS. 3 and 4.

Referring to FIG. 3, when the probe 30 is located above the positivesurface charges of a recording medium 40 including a dielectric layer47, the channel of minority carriers, electrons, is formed at the end ofthe tip 30 by the electric field generated from the surface charges.Therefore, the surface charges can be detected from currents that flowdue to the difference between the voltage of the source region 32 andthe voltage of the drain region 34.

Referring to FIG. 4, when the probe 30 is placed above the dielectriclayer 47 of the recording medium 40 and the same voltage is applied tothe source region 32, the drain region 34, and the body portion of thetip 30, the dielectric is polarized due to the electric field that isconcentrated between a bottom electrode 49 and the tip 30. Accordingly,information is recorded on the surface of the recording medium.

The method of fabricating the probe according to the present inventionrealizes a transistor having a short channel length at the tip, which isvertically formed at the end of the cantilever of the probe, by usingthe self-aligned fabrication that arranges the center of the channel atthe center of the tip. Thus, the method can be used to easily fabricatea nano-device using a scanning probe technique that detects a smallamount of surface charges existing in a small area on a recordingmedium.

In addition, when the information is recorded and reproduced on and froma large capacity and small sized recording apparatus utilizing thescanning probe technique by using the probe according to the presentinvention, the small amount of charges generated by polarizedferroelectrics can be easily reproduced and the charges can be easilyrecorded by generating polarization.

The drawings and specification of the invention are provided forillustration only and are not used to limit the scope of the inventionset forth in the appended claims.

For example, a person skilled in the art can manufacture an apparatusfor recording and reproducing information by using probes of variousshapes according to the present invention.

As described above, a method of fabricating a probe aligns the center ofa tip with the center of a channel existing between a source region anda drain region to realize a tip having a size of tens of nanometers.Thus, a nano-device can be easily manufactured using the probe havingthe tip.

While the present invention has been particularly shown and describedwith reference to exemplary embodiments thereof, it will be understoodby those of ordinary skill in the art that various changes in form anddetails may be made therein without departing from the spirit and scopeof the present invention as defined by the following claims.

1. A method of fabricating a probe, the method comprising: a first step of forming a first-shaped mask layer on a substrate and forming a source region and a drain region in regions of the substrate except for the region masked by the mask layer; a second step of patterning a first-shaped photoresist in a perpendicular direction to the mask layer and performing an etching process to form a second-shaped mask layer; and a third step of etching the regions of the substrate except for the region masked by the mask layer to form a probe.
 2. The method of claim 1, wherein the first-shaped mask layer is a striped-shaped mask layer.
 3. The method of claim 1, wherein the second-shaped mask layer is a square-shaped mask layer.
 4. The method of claim 1, wherein the first step further comprises performing a thermal diffusion process to reduce the distance between the source region and the drain region.
 5. The method of claim 1, wherein the ions are n-type ions, and the substrate is a p-type substrate.
 6. The method of claim 1, wherein the ions are p-type ions, and the substrate is an n-type substrate. 